Liquid paint systems are known that contain solvent and thus do not comply with the more recent requirements for freedom from emissions. Furthermore the more recent requirements insist on the greatest possible water-, oil-, dust-, dirt-repellent, and scratch-resistant surface properties, as well as improved slip properties of coated surfaces.
To this end the coating surfaces have previously been made hydrophobic by physically immersed or chemically bound perfluorinated additives. According to Barthlott et al., Planta 1997, 202, 1, an ultrahydrophobic layer property is understood to mean that the contact angle with a droplet of water placed on it is >130°.
For the coating of such hydrophobed surfaces, various coating agents based on polyurethanes, polyamides, polyesters, or polyacrylic acid derivatives were used, in particular polymers with perfluorinated side groups or blocks.
According to Thomas et al., Macromolecules 1997, 30, 2883, a coating agent containing perfluoroalkyl groups is known as a polymer solution based on acrylic acid esters containing perfluoroalkyl groups with alkylated and aromatic side groups and an isocyanate as a crosslinking agent/hardener. The surface hydrophobia is described with a contact angle of ≦117°. No ultrahydrophobic properties of the coated surface are achieved therewith.
According to Chapman et al., Macromolecules 1995, 28, 331, the synthesis of poly(amide urethane) block copolymers with perfluoroalkyl-containing side groups in solution is known for use as a coating agent. This method is very laborious and the contact angles achieved resulted in values of ≦116°.
Tirrell et al., Macromolecules 1996, 29, 3545, synthesized polyamide homopolymers that contain perfluoroalkyl-containing side groups, on the basis of perfluorinated glutamic acid derivatives for use as coating agents. Here too, only contact angles of ≦120° could be shown for the surface hydrophobia.
According to Ciradelli, F. et al., Progress in Organic Coatings 1997, 32, 43, long-chained perfluoroalkyl-containing side groups were inserted into acrylic acid ester copolymers and tested as coating agents. Contact angles of 130 to 146° could be achieved on the coated stone surfaces therewith. However, the synthesized copolymers were stated to be very unstable as far as their resistance to hydrolysis was concerned.
Similarly, Ming et al., Macromolecules 2000, 33, 6886, showed that polyesters with perfluoroalkylated end groups feature hydrophobic effects, but these are not stable over the long term.
According to U.S. Pat. No. 5,548,019 perfluoroalkylated chain blocks were inserted covalently into a polymer main chain in order to obtain aqueous and/or solvent-containing coating agents with perfluoroalkylated chain blocks. According to U.S. Pat. No. 5,674,951, perfluoroalkylated side groups have been inserted covalently into polyoxetanes with the same goal.
In both cases these polymers with polyurethanes in various perfluoroalkyl-containing percentages by weight, have been hardened from an aqueous or solvent-containing solution after application to the surface to be coated. In neither case could be achieved ultrahydrophobic properties.
According to U.S. Pat. No. 5,859,126, a method for the production of hydrophobic layers via an autoxidation and polymerization for the crosslinking of a urethane resin with unsaturated perfluoroalkylated fatty acid esters is known. The coated surfaces obtained therewith featured a contact angle of <130°.
Through U.S. Pat. No. 6,001,923 polyurethane coatings containing perfluoroalkyl groups are known that are obtained by reacting end-group-terminated perfluoroalkyl compounds or perfluoroalkylated polyether diols as a soft chain block with free diisocyanates in the presence of dibutyltin dilaurate and optionally binders containing hydroxyl groups to produce prepolymers.
According to WO 98/51727 the insertion of perfluoroalkyl compounds based on polyether diols has been implemented with a similar approach, which compounds were tested as coating agents.
In both cases, no ultrahydrophobic properties could be achieved.
A further method for attaching perfluoroalkylated side chains to the main chain is the synthesis of specific acrylic acid ester resins (WO 96/05172). A greater chemical stability is achieved thereby via the reaction of a diisocyanate coupling agent between the perfluoroalkylated alcohol unit and the OH-functionalized acrylic acid ester. Here too the coating agents are applied from the solution to the textile surface to be treated. Hydrophobic properties could be shown.
The disadvantage with all the known solutions is that no lasting ultrahydrophobic properties are achieved with the coated surfaces.